1. Field of the Invention
The present invention relates to an electric power steering apparatus.
2. Description of the Related Art
An electric power steering apparatus is structured such that a pinion shaft connected to a steering shaft is engaged with a rack shaft. A worm gear is provided in a drive shaft connected to an output shaft of an electric motor, and a worm wheel engaged with the worm gear is connected to the pinion shaft, whereby a torque of the motor is transmitted to the rack shaft to assist steering operation.
In the electric power steering apparatus, on respective tooth faces of the worm gear and the worm wheel, a proper backlash is set in view of requirement for working and operating. However, in the electric power steering apparatus, there is a case that a power transmitting direction is reversed due to operation of a steering wheel or a vibration input from a road surface. At a time of the reverse drive mentioned above, a tooth face at the back of the tooth face with which the worm gear or the worm wheel has been brought into contact suddenly moves to the extent of the backlash and collides with the opposing tooth face, whereby a striking sound is generated.
In the electric power steering apparatus, in the case that a stroke of the rack shaft is suddenly stopped such as when a tire rides over a curbstone during steering operation or other reasons, since the electric motor is going to continuously rotate due to inertia even when the electric motor stops supplying electric power, there is a risk that a propelling force of inertia of the electric motor damaging a torque transmission path.
An object of the present invention is to reduce a striking sound between tooth faces by reducing an impact force generated on the tooth faces of a gear provided in a torque transmission path of an electric motor, or to prevent the torque transmission path from being damaged due to a propelling force of inertia of the electric motor, in an electric power steering apparatus.
In accordance with the present invention, there is provided an electric power steering apparatus having
a pinion shaft connected to a steering shaft, the pinion shaft being engaged with a rack shaft.
A drive gear is provided in a drive shaft connected to an output shaft of an electric motor and
an intermediate gear is engaged with the drive gear, the intermediate gear being connected to the pinion shaft.
A torque transmission body made of an elastic body is interposed between the output shaft of the electric motor and the drive shaft.